Compared to other types of laser devices, semiconductor laser devices have many characteristics, such as high conversion efficiency, small volume, light weight, long lifetime, capable of direct modulation, liable to integrate with other semiconductor devices and so on. Such low power semiconductor laser devices have been widely used as information carrier in optical communication, optical storage, laser printing and other information fields. However, with the limits of wave guiding structure, chip packaging and other factors which leads poor beam quality and low power density, semiconductor laser devices are hard to be used as a direct optical source to apply for industrial process.
Recently, as the development of the semiconductor laser device technology, and under the promotion driving by the application of direct semiconductor laser industrial processing and the pumping demand of high-power optical fiber laser device, the semiconductor laser devices with high power and high beam quality develops rapidly. At the same time, the laser beam combining technology makes laser power increased multiply in the past few years. Nowadays, the power levels of optical fiber laser devices and direct semiconductor laser devices adopting beam combining technology have reached kilowatt stage.
Nowadays, the main methods of beam combination of semiconductor laser devices are coherent beam combination and incoherent beam combination. Coherent beam combination can effectively improve and increase the beam quality of output light of semiconductor laser array, but this technology is liable to be disturbed by external environment and it is hard to get a high-power stable output with same-phase and super-mode, and requires the beam combining array unit to be controlled strictly in many aspects, such as spectrum, phase position, amplitude, polarization state and so on. Thus, in the field of direct semiconductor laser device, incoherent technology is mainly employed.
Incoherent beam combination is used for making the output lasers of several laser devices transmit along a same direction to increase the power of laser multiply, wherein the power level is in direct proportion to the number of the laser devices. The incoherent technology comprises space beam combination, polarization beam combination and wavelength beam combination. Compared to coherent beam combination, incoherent beam combination has no requirements for phase position, spectrum, and amplitude, and is easy to be modulated, which is the main method of beam combination used in semiconductor laser devices nowadays. However, due to the restrictions brought by the mechanism of beam combination and the required optical devices, the above three incoherent beam combining methods all have certain defects, for example the beam quality and the luminance may not be improved effectively.
Space beam combination technology, such as introduced in U.S. Pat. No. 6,124,973 by Keming Du et al., which is used for stacking several semiconductor laser devices according to a certain spatial sequence to form a group of laser beams transmitting along a same direction, thereby to get high power laser output. As the space stacking cannot improve the beam quality, the resulting high-power laser output is generally and directly used in the occasions with lower beam quality requirements, such as serving as a pumping source of fiber laser device and the like.
Polarization beam combination technology mainly makes use of the polarization property of the laser device, to make two lasers with different polarization directions to combine and transmit along a same direction, such as introduced in the U.S. Pat. No. 8,427,749 by Jihua Du et al. Generally the polarization beam combination technology is used for making two laser beams or two laser beam combinations with mutually polarization directions to combine together, and is always used with other beam combination technologies.
Wavelength beam combination technology combines laser beams with different wavelengths by an optical unit such as a dichroscope, an optical grating and so on, which can increase power and luminance effectively, and is the main development direction of high-power direct semiconductor laser device nowadays. However, the present wavelength combination technology, no matter adopting a dichroscope, a volume Bragg grating or a diffraction grating, is always restricted by the spectrum, as different laser beams with different wavelengths are required to be independent from each other to keep enough wavelength intervals.
Antonio Sanchez-Rubio et al. from Lincoln Laboratory of Massachuarrangedts Institute of Technology put forward for the first time in the U.S. Pat. No. 6,192,062 that the grating-external cavity method can be used for realizing beam combination in external cavity as for semiconductor laser array or several fiber laser devices. After several decades research at home and abroad, the grating-external cavity spectrum beam combination (SBC) is proved to be the most effective beam combination technology to increase the beam quality of semiconductor laser and realize a high luminance output, and promotes the application in field of laser processing.
However, as for spectrum beam combination of the external cavity semiconductor laser array based on the U.S. Pat. No. 6,192,062 and similar technologies, the comprehensive consideration for the limits of diffraction grating dispersing ability, and the objects to increase beam quality and assure high enough efficiency etc, cause this type beam combining laser device to have wilder final output spectrum, longer whole light path and high requirement for precision adjustment and stability, which brings a certain inconvenience for the further development of the power of the direct output semiconductor laser device.